X76F641 datasheet(8/17 Pages) XICOR

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X76F641

Figure 7. Sequential Read

Data X

COMMAND

Read

Password

Read

Password

SDA

Data 0

If ACK, then

Wait tWC

ACK POLLING

ACK Polling

Repeated

COMMAND

Command

Password Matches

7025 FM 12

PASSWORDS

The sequence in Figure 8 shows how to change (pro-

gram) the passwords. The programming of passwords is

done twice prior to the nonvolatile write cycle in order to

verify that the new password is consistent. After the eight

bytes are entered in the second pass, a comparison

takes place. A mismatch will cause the part to reset and

enter into the standby mode.

Data ACK polling can be used to determine if a password

has been loaded correctly, however the data ACK com-

mand must be issued less than 2ms after the stop bit.

After this time, it cannot be determined if the password

has been loaded correctly, without trying the new pass-

word. To determine if the new password has been loaded

correctly the data ACK polling command is issued imme-

diately following the stop bit. If it returns an ACK, then the

two passes of the new password entry do not match. If it

returns a "no ACK" then the passwords match and a high

voltage cycle is in progress. The high voltage cycle is

complete when a subsequent data ACK command

returns an "ACK".

There is no way to read any of the passwords.

Figure 8. Change Passwords

COMMAND

Old

Password

Old

Password

SDA

New

Password

New

Password

New

Password

If ACK, then

Two bytes of “0”

Wait tWC

ACK POLLING

ACK Polling

Repeated

COMMAND

Command

Password Matches

If immediate ACK,

then New Password error

Data ACK

Polling

If immediate NACK,

then New Password OK

followed by ACK after ~5ms

7025 FM 13

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